System and method of cell block voltage analytics to improve balancing effectiveness and identify self-discharge rate

Abstract

A battery management unit includes a cell balancing module to perform cell balancing between a cells in a battery cell stack, and a controller operable to determine, during a first charge cycle, that the first cell has reached an over-voltage threshold before the second cell, to determine, during a discharge cycle, that the first cell has reached an under-voltage threshold before the second cell, to identify the first cell as having a lower capacity than the second cell based upon the determination that the first cell reached the over-voltage threshold before the second cell and upon the determination that the first cell reached the under-voltage threshold before the second cell, and to prevent, during another charge cycle, the cell balancing module from performing cell balancing on the first cell based upon the first cell being identified as having the lower capacity than the second cell.

What is claimed is: 
     
       1. A battery management unit comprising:
 a cell balancing module programmed to perform cell balancing between a first battery cell of a plurality of battery cells in a battery cell stack and a second battery cell of the plurality of battery cells, wherein in performing the cell balancing, the cell balancing module is further programmed to: 
 charge the first battery cell and the second battery cell until a first one of the first or second battery cells is charged to an over-voltage threshold; 
 determine if the other one of the first or second battery cells is charged to less than an over-voltage hysteresis threshold, wherein the over-voltage hysteresis threshold is less than the over-voltage threshold; 
 halt the charging of the first battery cell and the second battery cell in response to determining that the other one of the first or second battery cells is charged to less than a voltage hysteresis threshold; and 
 discharge the first one of the first or second battery cells to the overvoltage hysteresis threshold; and 
 a controller programmed to: 
 determine, during a first charge cycle of the battery cell stack, that the first battery cell has reached the over-voltage threshold before the second battery cell; 
 determine, during a discharge cycle of the battery cell stack, that the first battery cell has reached an under-voltage threshold before the second battery cell; 
 identify the first battery cell as having a lower capacity than the second battery cell based upon the determination that the first battery cell reached the over-voltage threshold before the second battery cell and upon the determination that the first battery cell reached the under-voltage threshold before the second battery cell; and 
 prevent, during a second charge cycle, the cell balancing module from performing cell balancing on the battery cell stack based upon the first battery cell being identified as having the lower capacity than the second battery cell. 
 
     
     
       2. The battery management unit of  claim 1 , further comprising:
 a memory including a cell charge history table that stores state of charge information for the plurality of battery cells; 
 wherein the controller is further programmed to: 
 store a first entry in the cell charge history table, the first entry indicating a first state of charge of the first battery cell when the first battery cell reached the over-voltage threshold, and including a first timestamp; and 
 store a second entry in the cell charge history table, the second entry indicating a second state of charge of the first battery cell when the first battery cell reached the under-voltage threshold, and including a second timestamp; and 
 wherein identifying the first battery cell as having the lower capacity is further based upon the first entry and the second entry. 
 
     
     
       3. The battery management unit of  claim 2 , wherein the second entry further indicates that the first cell has the lower capacity. 
     
     
       4. The battery management unit of  claim 2 , wherein the controller is further programmed to:
 Determine, during the first charge cycle, that the second battery cell has not reached the over-voltage hysteresis threshold in response to determining that the first battery cell has reached the over-voltage threshold; and 
 direct, during the first charge cycle, the cell balancing module to perform cell balancing on the first battery cell in response to determining that the second battery cell has not reached the over-voltage hysteresis threshold. 
 
     
     
       5. The battery management unit of  claim 4 , wherein the controller is further programmed to:
 store a third entry in the cell charge history table, the third entry indicating a third state of charge of the second battery cell when the first battery cell reached the over-voltage threshold, and including a third timestamp; 
 wherein directing the cell balancing module to perform cell balancing on the first battery cell is in further response to the third entry. 
 
     
     
       6. The battery management unit of  claim 2 , wherein:
 the controller includes a communication port and an alert output; the battery management unit is coupled to a host system; and 
 the controller is further programmed to communicate the first entry and the second entry to the host system via the communication port. 
 
     
     
       7. The battery management unit of  claim 6 , wherein the controller is further programmed to provide an alert to the host system on the alert output, the alert indicating that the controller prevented the cell balancing module from performing cell balancing on the first battery cell. 
     
     
       8. The battery management unit of  claim 1 , wherein the controller is further programmed to:
 determine, during a third charge cycle of the battery cell stack, that the first battery cell and the second battery cell have reached the over-voltage threshold before a third battery cell of the plurality of battery cells; 
 determine, during the third charge cycle, that the third battery cell has not reached the over-voltage hysteresis threshold in response to determining that the first battery cell and the second battery cell have reached the over-voltage threshold; and 
 direct, during the third charge cycle, the cell balancing module to perform cell balancing on the first battery cell and the second battery cell in response to determining that the third battery cell has not reached the over-voltage hysteresis threshold. 
 
     
     
       9. A battery management unit comprising:
 a cell balancing module programmed to perform cell balancing between a first battery cell of a plurality of battery cells in a battery cell stack and a second battery cell of the plurality of battery cells, wherein in performing the cell balancing, the cell balancing module is further programmed to: 
 charge the first battery cell and the second battery cell until a first one of the first or second battery cells is charged to an over-voltage threshold; 
 determine if the other one of the first or second battery cells is charged to less than an over-voltage hysteresis threshold, wherein the over-voltage hysteresis threshold is less than the over-voltage threshold; 
 halt the charging of the first battery cell and the second battery cell in response to determining that the other one of the first or second battery cells is charged to less than a voltage hysteresis threshold; and 
 discharge the first one of the first or second battery cells to the over-voltage hysteresis threshold; 
 a memory including a cell charge history table that stores state of charge information for the plurality of battery cells; and 
 a controller programmed to: 
 determine, during a first charge cycle of the battery cell stack, that the first battery cell has reached the over-voltage threshold before the second battery cell; 
 store a first entry in the cell charge history table, the first entry to indicate a first state of charge of the first battery cell when the first battery cell reached the over-voltage threshold, and to include a first timestamp; 
 determine, during a discharge cycle of the battery cell stack, that the first battery cell has reached an under-voltage threshold before the second battery cell; 
 store a second entry in the cell charge history table, the second entry to indicate a second state of charge of the first battery cell when the first battery cell reached the under-voltage threshold, to indicate that the first cell has the lower capacity, and to include a second timestamp; 
 identify the first battery cell as having a lower capacity than the second battery cell based upon the first entry and the second entry; and 
 prevent, during a second charge cycle, the cell balancing module from performing cell balancing on the battery cell stack based upon the first battery cell being identified as having the lower capacity than the second battery cell. 
 
     
     
       10. The battery management unit of  claim 9 , wherein the controller is further programmed to:
 determine, during the first charge cycle, that the second battery cell has not reached the over-voltage hysteresis threshold in response to determining that the first battery cell has reached the over-voltage threshold; and 
 direct, during the first charge cycle, the cell balancing module to perform cell balancing on the first battery cell in response to determining that the second battery cell has not reached the over-voltage hysteresis threshold. 
 
     
     
       11. The battery management unit of  claim 10 , wherein the controller is further programmed to:
 store a third entry in the cell charge history table, the third entry indicating a third state of charge of the second battery cell when the first battery cell reached the over-voltage threshold, and including a third timestamp; 
 wherein directing the cell balancing module to perform cell balancing on the first battery cell is in further response to the third entry. 
 
     
     
       12. The battery management unit of  claim 9 , wherein:
 the controller includes a communication port and an alert output; the battery management unit is coupled to a host system; and 
 the controller is further programmed to communicate the first entry and the second entry to the host system via the communication port. 
 
     
     
       13. The battery management unit of  claim 12 , wherein the controller is further programmed to provide an alert to the host system on the alert output, the alert indicating that the controller prevented the cell balancing module from performing cell balancing on the first battery cell. 
     
     
       14. The battery management unit of  claim 9 , wherein the controller is further programmed to:
 determine, during a third charge cycle of the battery cell stack, that the first battery cell and the second battery cell have reached the over-voltage threshold before a third battery cell of the plurality of battery cells; 
 determine, during the third charge cycle, that the third battery cell has not reached the over-voltage hysteresis threshold in response to determining that the first battery cell and the second battery cell have reached the over-voltage threshold; and 
 direct, during the third charge cycle, the cell balancing module to perform cell balancing on the first battery cell and the second battery cell in response to determining that the third battery cell has not reached the over-voltage hysteresis threshold. 
 
     
     
       15. A battery management unit comprising:
 a cell balancing module programmed to perform cell balancing between a first battery cell of a plurality of battery cells in a battery cell stack and a second battery cell of the plurality of battery cells, wherein in performing the cell balancing, the cell balancing is further programmed to: 
 charge the first battery cell and the second battery cell until a first one of the first or second battery cells is charged to an over-voltage threshold; 
 determine if the other one of the first or second battery cells is charged to less than an over-voltage hysteresis threshold, wherein the over-voltage hysteresis threshold is less than the over-voltage threshold; 
 halt the charging of the first battery cell and the second battery cell in response to determining that the other one of the first or second battery cells is charged to less than a voltage hysteresis threshold; and 
 discharge the first one of the first or second battery cells to the over-voltage hysteresis threshold; 
 a memory including a cell charge history table that stores state of charge information for the plurality of battery cells; and 
 a controller programmed to: 
 determine, during a first charge cycle of the battery cell stack, that the first battery cell has reached the over-voltage threshold before the second battery cell; 
 determine, during the first charge cycle, that the second battery cell has not reached the over-voltage hysteresis threshold in response to determining that the first battery cell has reached the over-voltage threshold; 
 direct, during the first charge cycle, the cell balancing module to perform cell balancing on the first battery cell in response to determining that the second battery cell has not reached the over-voltage hysteresis threshold; 
 store a first entry in the cell charge history table, the first entry indicating a first state of charge of the first battery cell when the first battery cell reached the over-voltage threshold, and including a first timestamp; 
 determine, during a discharge cycle of the battery cell stack, that the first battery cell has reached an under-voltage threshold before the second battery cell; 
 store a second entry in the cell charge history table, the second entry indicating a second state of charge of the first battery cell when the first battery cell reached the under-voltage threshold, and including a second timestamp; 
 identify the first battery cell as having a lower capacity than the second battery cell based the first entry and the second entry; and 
 prevent, during a second charge cycle, the cell balancing module from performing cell balancing on the battery cell stack based upon the first battery cell being identified as having the lower capacity than the second battery cell. 
 
     
     
       16. The battery management unit of  claim 15 , wherein the controller is further programmed to:
 store a third entry in the cell charge history table, the third entry indicating a third state of charge of the second battery cell when the first battery cell reached the over-voltage threshold, and including a third timestamp; 
 wherein directing the cell balancing module to perform cell balancing on the first battery cell is in further response to the third entry. 
 
     
     
       17. The battery management unit of  claim 15 , wherein:
 the controller includes a communication port and an alert output; the battery management unit is coupled to a host system; and 
 the controller is further programmed to communicate the first entry and the second entry to the host system via the communication port. 
 
     
     
       18. The battery management unit of  claim 17 , wherein the controller is further programmed to provide an alert to the host system on the alert output, the alert indicating that the controller prevented the cell balancing module from performing cell balancing on the first battery cell. 
     
     
       19. The battery management unit of  claim 15 , wherein the controller is further programmed to:
 determine, during a third charge cycle of the battery cell stack, that the first battery cell and the second battery cell have reached the over-voltage threshold before a third battery cell of the plurality of battery cells; 
 determine, during the third charge cycle, that the third battery cell has not reached the over-voltage hysteresis threshold in response to determining that the first battery cell and the second battery cell have reached the over-voltage threshold; and 
 direct, during the third charge cycle, the cell balancing module to perform cell balancing on the first battery cell and the second battery cell in response to determining that the third battery cell has not reached the over-voltage hysteresis threshold.